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Pretty new round here, I'll just start off with a bit of a back story.
I just turned 18, my girlfriend is 16 (nearly 17) some think it's a pretty bad age gap but most people honestly don't seem to care. My girlfriend lives 50 miles away from me and I see her every weekend. Her mum's family are pretty fcking awesome to be honest with you - I've only been with my girlfriend for around 6 months but they've basically taken me in as their own. I'm fully comfortable with them all. Her dad's family is a completely different story.
Her parents split a while ago but they're blatantly still having a sh*g here and there behind my girlfriend's stepdad's back. It's all a bit of a sh!tstorm and her dad always finds a way to blame me for seeing her so often.
I've suggested multiple times that I can back off and give her more time with her dad (because apparently staying at his house 3 nights a week isn't enough) but her mum's family (and my girlfriend) are all adamant that I don't have to do that.
I'm going on holiday with her in a couple of days and her dad knows about it. It will literally be my girlfriend and I in a hotel room together for two nights. Her dad doesn't like me whatsoever. The first time he met me I shook his hand and did all the cliche sh!t that everybody recommended to me but I suppose he's just overprotective. He doesn't do anything for my girlfriend, and I often find myself paying for things HE should be paying for (and for an apprentice on just under a grand a month, it can be a bit of a pain in the ass).
The first time he met me he pointed at the sofa and said "you better be sleeping there" and every time he leaves he comes up to me, doesn't shake my hand or anything and just says "watch what you're doing".

Basically he's about 5ft5 and pretty fat. He's got tattoos so he thinks he's the ****. I'm not physically intimidated by him whatsoever but I'm scared that he's a bit of a psycho and he could probably arrange for stuff to happen to me if I really pissed him off.
He's not my girlfriend's legal guardian, so LEGALLY, is there anything he can do about me taking her away for two nights? Her mum (her legal guardian) has already confirmed that she's perfectly fine with it. I'm just getting pissed off because whilst I understand he's protective of his daughter, I've done nothing to piss him off. I know that he has small-man syndrome and he's scared of his own reflection but what can he legally do about me taking his daughter on two nights away?

Sorry for rambling, I can hardly construct a sentence but yeah. Any advice would be appreciated.
Thanks